Parkinson's Disease (PD) is a progressive, neurodegenerative disease, which affects over 1,000,000 Americans. In an NIH-supported phase II trial, our group demonstrated that treatment of patients with early, untreated PD with high dosages of coenzyme Q10 (300, 600 and 1200 mg/d) was safe and well tolerated and that there was a positive trend for treatment to slow the progressive impairment as measured by the Unified Parkinson Disease Rating Scale (UPDRS). In pre-specified secondary analyses, we noted that the highest dosage of coenzyme Q10 was the most effective dosage and that treatment with coenzyme Q10 helped the PD patients maintain independence, as measured by Schwab and England Scale. In the proposed study, we will conduct a prospective, randomized, placebo-controlled, double-blind phase clinical trial of coenzyme Q10 to attempt to confirm and extend the results of our phase II study. We propose to enroll 600 subjects who have early PD and do not yet require treatment with dopaminergic agents. Subjects will be randomly assigned to receive placebo, coenzyme Q10 1200 mg/d or 2400 mg/d, evaluated at screening, baseline, months 1, 4, 8, 12, and 16 visits and assessed with the UPDRS. The investigator will determine whether the subject has reached disability requiring treatment with a dopaminergic agent. Our primary analysis will undertake to confirm the benefit found in our phase II study by analyzing the change in total UPDRS score to the point that the subjects reach disability requiring treatment with a dopaminergic agent or to the 16 month visit. We will also analyze the Schwab and England Scale and the PD Quality of Life Scale data collected to the point that the subjects reach disability requiring treatment with a dopaminergic agent or to the 16 month visit. We will determine the mean plasma coenzyme Q10 levels at baseline and at visits 1, 8 and 16 months, and determine whether the mean correlates with reduction in worsening of the total UPDRS score.